Depth of field is a technique borrowed from film cameras to set off what is subject and what is background:
Open the file
6907_11_Blender Island.blend.In the Outliner window just above the Properties window, select Camera.Depth of Field with theLMB.
In the header of the right-hand 3D View window, select View, then Cameras, and then Set Active Object as Camera.
You can use the mouse wheel to make the camera area fill the window.
Look at the Layers controls in the 3D View header. The Sky is in Layer 10. Press Shift+LMB over Layer 10 so that all layers with objects will render.
Press F12 to render the scene. It looks similar to the previous image, but without the people. You can use Ctrl+MMB and use the mouse to fill the window with the image after it has rendered. Look at it and see how everything in the image is in focus. Zoom into the house so you can see the tiles on the roof. Do not press Esc to get rid of the image.
In the Timeline window, select...